ACC=Advanced Clock Calibration, a technology present in some of the AMD 700 Southbridge chip series that enables achievement of higher CPU clock speeds for the K10-based processors

One part of ACC is in conforming SouthBridge chip ( like SB750 and later), other is in conforming CPU ( Like Phenom I or II ).

SB chip can regulate certain parameters in CPU through special interface ( reportedly 6 pins ), which can enable CPU to be able to overclock to higher frequencies or to use less power at nominal frequencies.

ACC can be regulated on each core separately from the others.

As I understand, much of whole shebang is kept in secret, but it would be nice to know at least the bit, which would enable me to make boot-time or Linux kernel driver for setting/testing it.

I have sifted through aforementioned "BIOS and Kernel Developer's Guide" and other documents, SB7xx documentation etc, but ACC is not even mentioned anywhere...

It's looking like this information is very secret. I can't find it in any NDA BKDG documents or other NDA docs. But, I've sent a question to some of our very bright BIOS developers to see if they have the information and if they have it, I have to get clearance to share it with the public... so, stay tuned, but be prepared for the likelyhood that I won't be able to share it.

"Due to the nature of ACC a system reboot is required to toggle it, therefore ACC cannot be enabled/disabled at runtime. All systems that implement the ACC feature do it with a BIOS control, any other agent attempting to modify its state would conflict with the BIOS which regains control of the system when the required reboot occurs. I am sorry but this feature cannot be easily be controlled by a user application"